Rank: worked on the Zhukov as Lieutenant junior grade, worked as an Diagnostic Engineer on the U.S.S. Enterprise NCC-1701-E. Later on in life he was promoted to the rank of Commander (see Voyager episode End Game). In the video game Star Trek: Elite Force II, Barclay was temporary chief engineer on the Enterprise-E.

Reginald Endicott Barclay III first worked from 2362 on the.S.S. Zhukov NCC-62136 under Capt. Gleason as a Lieutenant junior grade. In 2366 he was transferred to the Enterprise. In 2374 he transferred to the Starfleet's Communications Research Center where he worked with the Midas Array. Barclay worked there under supervision of Commander Peter Harkins with the Mutara Interdimensional Deep-Space-Transponder Array System. In 2376 while working on the pathfinder project he was successful in reaching Voyager. Later in life (year uncertain at least before 2404) he was promoted to the rank of Commander. Besides his usual work he conducts lectures to cadets at Starfleet's Communications.

Barclay isn't married but he did date some girls, like Leosa for instance. But he never had any luck with women. Leosa turned out to be a Ferengi dabogirl who only wanted to help the Ferengi to steal Barclay's hologram for a small fee. She wasn't a teacher as she told him and she didn't love him at all. She only used him to get the information she needed and broke up with him as soon as she had it, leaving Barclay heartbroken. Later on during an episode in Star Trek Voyager we learned he was dating a starfleet admiral's daughter named Hope.

Barclay suffers from holodeck addiction, hypochondria and transporter phobia, he was forced to use the transporter though in 2369 when he was forced to participate in the U.S.S. Yosemite rescue mission. Barclay once thought he was suffering from Terellian Death Syndrome. He also stammers. In the Nth Degree episode he acquires superhuman intelligence from contact with a probe belonging to an alien race and takes over the ship's computer to save it when the Cytherian probe becomes dangerous. He gradually overcomes his holodeck addiction and loses his transporter-phobia when he's forced to use one in the episode Realm of Fear. In the episode Genesis his hypochondria is cured once and for all on stardate 47653.2 when he gets treated for some type of flu with synthetic T-cells and than gets a rare disease that turns into a virus that makes the crew revert to earlier evolutionary stages, (Barclay turns into a spider). After Data cures it, Doctor Crusher names it Barclay's Protomorphosis Syndrome. So according to Barclay he was cured from all of those things (yeah right and we have to believe that?). He does gain more confidence in his later years and that makes him loose his stammering. It does come up briefly when the Doctor (who than names himself Joe) tries to figure out where Admiral Janeway is. Barclay knows but doesn't want to tell, he than starts to stammer again. Apparently Barclay's stammering returns when he tells a lie. That gives Joe enough prove that Barclay knows where she is and he is able to get the information out of him.

Barclay owned a pet cat (a white Persian tomcat) when he was stationed at Starfleet's Communications Research Center in the year 2374. He named that cat Neelix after Neelix from Voyager because he thought Neelix was feline, he even thought the real Neelix purred! Lt. Barclay had a way with animals, it seems he especially likes cats. According to Data, his female cat Spot only allowed Barclay to handle her besides Data. She attacked and scratched other crewmembers on the Enterprise who tried to look after Spot (according to STTNG episode Genesis). That's why Barclay looked after Spot while she was pregnant and Data had to go away on a mission.

Besides staring in 5 STTNG episodes he was mentioned in the episode 'A Fistful Of Data's'. He helped Alexander (Worf's son) construct a holodeck program for his father. It was the old west period from Earth's history. But we never got to see Barclay.